Field of the Invention
The present invention relates to an optical system, and an optical apparatus including the same.
Description of the Related Art
Japanese Patent Laid-Open Nos. (“JPs”) 2011-13469 and 2009-198855 each propose a configuration that has a small F-number, is usable for a range from a wide angle of view to a normal angle of view, and disposes a lens unit having a positive or negative refractive index on an object side of a so-called Gauss-type optical system that includes lens units each having a positive refractive power that are disposed approximately symmetrically with respect to an aperture diaphragm.
In order for such an optical system with a small F-number to achieve a high optical performance, it is important to sufficiently correct the curvature of field, astigmatism, and chromatic aberration. The Gauss-type optical systems disclosed in JPs 2011-13469 and 2009-198855 can sufficiently reduce the astigmatism by making small a Petzval sum, but may fail to sufficiently reduce the chromatic aberration (specifically, longitudinal chromatic aberration and lateral chromatic aberration).